1. Field of the Invention
The present invention relates to a portable telephone with an extendible antenna, and more particularly, to a method for automatically switching an antenna mode according to a received signal strength.
2. Description of the Related Art
In general, a portable telephone employs an extendible antenna which can be extended from the top of the telephone. The extendible antenna is extended (or stretched out) in an external antenna mode, and retracted (or unstretched) in an internal antenna mode. Both manual and automatic antenna mode switching techniques have been used to implement the extension/retraction operations.
In the manual antenna mode switching technique, the portable phone user extends and retracts the antenna by hand. The user typically extends the antenna when reception sensitivity is poor during a call. This method is inconvenient to the user, and may also cause a noise problem. That is, if the user extends the antenna by hand when a received signal strength indication (RSSI) value is poor, noise may be introduced to the receiver when the antenna is physically touched. Worse, the call may be disconnected as a result of the added noise. The RSSI value, which is measured by circuitry within the portable phone, is a measure of the strength of the communication signal transmitted by the base station to the portable phone.
With the automatic antenna mode switching technique, the antenna is automatically extended when the user initiates the call and automatically retracted when the user terminates the call. In this case, the antenna is extended and retracted by an antenna moving mechanism (actuator) employing a motor. A drawback to this technique, however, is that the antenna is automatically extended when the call is initiated, regardless of the user's intention. That is, the antenna is extended even when the RSSI value is satisfactory. Such unconditional extension of the antenna when the call is initiated may annoy the user, or result in damage to the antenna due to carelessness of the user.